addFieldToFilter in magento2 returning same data everytime

addfieldtofilter in magento2 behaving weirdly

I have code

   foreach($  userDetails as $  singleUserDetails) {                            $  userid=$  singleUserDetails['user_id'];             var_dump($  userid);//everytime values changes 1,2,3             $  users = $  this->userCollection ->addFieldToFilter('user_id',$  userid);              var_dump($  users->getData());// output:                                  array('id'=>1,'user_id'=>1,'user_name'=>'a');                                  array('id'=>1,'user_id'=>1,'user_name'=>'a');                                  array('id'=>1,'user_id'=>1,'user_name'=>'a');                      } 

same code If I write with passing value then it gives correct data

    foreach($  userDetails as $  singleUserDetails) {                            $  userid=$  singleUserDetails['user_id'];             var_dump($  userid);//everytime values changes 1,2,3             $  users = $  this->userCollection->addFieldToFilter('user_id',3);              var_dump($  users->getData());// output: array('id'=>3,'user_id'=>3,'user_name'=>'c');                       }